Actually, the EGR works most of the time in low idle, and low demand stituations, like warm up and sitting in traffic. It helps to keep the emissions down by reburning un-used hyrocarbons. It is a known fact that with out this thing, motors make more power, but I dont think we need to touch on the legallity of tampering with emissions equipment. Now if you are losing power, that means that it is stuck open, and is constantly burning exhuast fumes, and the more load, the more fumes, the less power. If it didnt pass emissions, it is stuck closed. Most of these happen do to carbon build up, which in this part, is unpreventable. Each brand sets thiers up differently, thus I cant say whether the vaccuum should be constant or variable. But MY thought is, that most of them, close as the enigine loads, thus, increasing vaccuum. Basically, the more air an engine PULLS into it self, the more likley that EGR is closed..

Hope that helps...

Chase

By the way, not fact on ALL EGRs...